1. Field of Invention
This invention relates to a security device and more particularly to a housing constructed to prevent external access to sensitive data stored therein.
2. Description of the Prior Art
Several known prior art techniques have been proposed for the construction of a housing which prevents access to the sensitive data stored therein.
International patent application No. WO 84/04614 discloses a data security device which includes a container formed of a brittle material such as prestressed glass and which includes a data processor, a volatile CMOS RAM memory device for storing encryption key data, and a battery forming the power supply for the memory device. The container consists of a housing and a lid. The battery is connected to the memory device by a power supply conductor formed in a winding path configuration on the interior surfaces of the housing and the lid, the parts of the power supply conductor on the housing and lid being connected by pairs of contacts at the joint faces between the housing and the lid. The conductor is formed by an evaporated metal thin film material. The power supply conductor pattern is bifilar and the parts of the conductor are interleaved with additional conductors on the interior surfaces of the housing and lid which are earthed or connected to a voltage source. Thus, if the power supply conductor is interrupted or connected to either of the additional conductors the power supply to the volatile RAM would be so much altered that the data in the RAM would be destroyed. The known device has the disadvantage of a relatively low level of security since the width of the power supply conductor provided on the housing must be maintained sufficiently great to enable the provision of an adequate power supply to the memory device. Such relatively wide conductors are subject to the possibility of penetration. For example, it could be possible to produce a hole of sufficiently small diameter to maintain a conductive path in a relatively wide power supply conductor, yet enable unauthorized access to the memory device via the hole. Furthermore, the thin film technology utilized in the manufacture of the known device results in high device cost.
German Offenlegungsschrift No. 3023427 discloses a mobile data storage unit which includes a plurality of memory devices within a closed container formed by a housing and a lid. Located within the material forming the walls of the container are a plurality of differential pressure sensing devices connected to closed channels also located in the walls of the container, such that any attempt to break into the container which disrupts the pressure in the closed channels is detected by the pressure sensing devices and causes the operation of a relay to provide an erase signal to erase the contents of the memory devices. Also located within the material forming the walls of the container are a pair of thin conductors, which run in an arbitrary configuration through the housing and the lid, and are connected to a power source and the relay. Any external influence which breaks either of these thin conductors also causes the relay to provide an erase signal to erase the contents of the memory devices. However, this known device is of complex and expensive construction resulting from the provision of the closed channels and pressure sensing devices. Furthermore, the possibility exists of forming a small diameter hole into the interior of the unit without interrupting either of the pair of thin conductors. This, the degree of security achievable with this known unit is also limited.
It is thus an object of the present invention to provide a data security device wherein the aforementioned disadvantages are alleviated.